Em Wed, Feb 04, 2009 at 05:16:18PM +0100, Petr Machata escreveu:
.debug_arange analysis shows that there's a lot of holes in .text. Turns
out these are NOP runs (for alignment purposes, I guess). First, is it
OK for the producer to leave NOP runs alone? If yes, dwarflint
shouldn't warn about it, but then there is a problem of how to detect
I think we can assume that the compiler actually emits literal "NOP"
instructions for padding purposes (i.e. not one of these contraptions
that look like they do something). But most of the time, we won't even
see contents of .text, will we? We are dealing with stripped
debuginfo-only files. Or are we going to do our debuginfo
transformation business on full files?
ftrace in the Linux kernel uses NOPs for leaving space for dynamic code
patching, to insert calls to mcount, etc.
I guess the alternatives code in the Linux kernel also uses NOPs to
provide a dynamicly optimizable kernel depending on the processor the
kernel is booted on.
If curious, take a look at:
arch/um/sys-x86_64/shared/sysdep/system.h Look at rdtsc.
in the Linux sources :-)